The invention relates to a frame for a color selection mechanism for use in a cathode ray tube.
A conventional color selection mechanism 1 for a cathode ray tube (CRT) is shown in FIG. 1. From FIG. 1 it can be seen that the color selection mechanism 1 comprises an aperture grill 10 which includes a number of narrow belt-shaped grid elements 8, which are commonly known as tapes and which define slit shaped apertures 9 between adjacent tapes 8. The aperture grill 10 is supported on a metallic frame 6 which includes two support members 2, 3 which are coupled together by two frame members 4,5. The aperture grill 10 is welded to the support members 2, 3 at opposite edges so that the tapes 8 extend from the support member 2 to the support member 3.
The color selection mechanism 1 also includes two damper wires 12 which are mounted by mounting members 14 to the frame members 4, 5 so that the damper wires 12 are stretched across the tapes 8, as shown in FIG. 1. The damper wires 12 are stretched across the tapes 8 such that the damper wires 12 are in contact with each of the tapes 8 (see FIG. 2) to minimize vibration of the tapes 8 when the color selection mechanism is installed in a CRT. This is especially important in situations where the color selection mechanism is located near a speaker. For example, in a television or a computer monitor with attached speakers, as the sound from the speakers tends to induce vibration of the tapes 8. This vibration results in distortion of the image on the CRT if the damper wires 12 are not present.
In addition, the color selection mechanism 1 includes four spring loaded clips 15 mounted to each of the support members 2, 3 and the frame members 4, 5 by spring holders 13. The spring clips 15 permit mounting of the colour selection mechanism within a CRT.
Each of the support members 2, 3 is formed with a radius of curvature R in the Z direction, as shown in FIG. 3. In conventional colour selection mechanisms for conventional CRTs, the radius of curvature R was typically of the order of 1000 mm or less. Therefore, the radius of curvature was sufficiently small to ensure that the damper wires 12 were in contact with all of the tapes 8 even if there was an error in the alignment of one of the tapes. For example, if one of the tapes was twisted.
However, more recently, there has been a trend towards flat screen CRTs in which the radius of the curvature is at least 4000 mm and can be as high as 8000 mm, or greater. With a large radius of curvature such as this, small errors in alignment of the tapes 8 (for example, twisting of the tapes 8) can cause the damper wires not to touch tapes that are adjacent to the twisted tapes. This is a particular problem at the edges of the aperture grill where the edge tapes 8A are wider to provide additional support for the damper wires 12 at the edges of the aperture grill 10 adjacent to the damper wire supports 14. Typically, the edge tape 8A at each side of the aperture grill is approximately ten times the width of the other tapes forming the aperture grill. Hence, a small twisting of one of the edge tapes 8A can cause the damper wires 12 not to contact tapes 8B adjacent to the edge tapes 8A, as shown in FIG. 4.
Therefore, this can result in vibration of the tapes 8B not contacted by the damper wires during use which can result in distortion of the image on the CRT.
In accordance with a first aspect of the present invention, there is provided a color selection mechanism for a color CRT which includes
a frame to which a color selection electrode thin plate is to be applied, and
a color selection electrode thin plate,
characterized in that
a surface of said frame to which said color selection electrode thin plate is to be applied is formed from a face represented by a first and a second function in a longitudinal direction from the center of said frame, and said surface is leftwardly and rightwardly symmetrical with respect to a center axis thereof.
Preferably, the first function is a polynomial of degree three or more.
Preferably, the second function is a polynomial of degree two.
Typically, the transition from the first to the second function occurs at 10 to 15 color selection electrode pitches inwardly from an edge of the color selection electrode thin plate.
In accordance with a second aspect of the present invention, there is provided a frame for a color selection mechanism for a color CRT, the frame being adapted to have a color selection thin plate attached thereto, and the frame comprising two spaced apart support members, the support members each having a mounting surface, each of the mounting surfaces having a central surface portion with a first radius of curvature and end surface portions with a second radius of curvature, the second radius of curvature being smaller than the first radius of curvature.
Typically, the end surface portions extend for less than approximately 30 mm from the end of the mounting surfaces, preferably for less than 20 mm, and most preferably, extend for between 5 mm to 15 mm from the end of the mounting surfaces.
Typically, the first radius of curvature is greater than or equal to 4000 mm and the second radius of curvature is less than 1000 mm. Preferably, the second radius of curvature is less than 500 mm.
In accordance with a third aspect of the present invention, there is provided a color selection mechanism for a color CRT comprising a frame in accordance with the second aspect of the invention, a color selection thin plate mounted on the mounting surfaces and a vibration reducing member extending across the color selection thin plate.
In accordance with a fourth aspect of the present invention, there is provided a cathode ray tube comprising a color selection mechanism in accordance with the first or the third aspect of the invention.